The goal of this research project is to elucidate the functions of parasite proteases in the growth and maturation of the malarial parasite Plasmodium falciparum. The goal is related to a long- range objective of developing new antimalarial drugs targeted at parasite proteases, especially proteases involved in parasite-host interactions. The specific aims of this project are 1) to characterize acid and neutral proteases and to determine their roles in the degradation of hemoglobin; 2) to determine there roles of ATP-dependent and ATP-independent non-lysosomal proteolysis in the development of P.falciparum; 3) to elucidate the site of action of chloroquine; 4) to determine the roles of proteases in merozoite-host interactions. The following hypotheses will be tested: 1. Digestion of host cytosol by malarial parasites involves acid proteases in the parasite's food vacuole but also involves non- lysosomal pathways for the degradation of hemoglobin. 2. Chloroquine interferes with the digestion of hemoglobin by diverting hemin from sequestration into malarial pigment. The actual inhibitor of parasite growth is free hemin which inhibits proteolysis. 3. Chloroquine resistance results from mutations which increase the efficiency of sequestration of hemin into malarial pigment. 4. Surface proteases of merozoite-stage parasites are active participants in the process of invasion of erythrocytes by P.falciparum. Parasite proteases will be purified by HPLC procedures and will be characterized Cytochemical and immunocytochemical studies of cellular proteases will be carried out. Proteases will be carried out. Proteases will be isolated from various morphological states of the intraerythrocytic parasite.